1. Field of the Invention
The present invention relates to an electric steering lock device configured to electrically lock rotation of a steering wheel of a parked vehicle.
2. Description of the Related Art
In recent years, as protection against theft, some vehicles are equipped with an electric steering lock device configured to electrically lock rotation of a steering wheel while the vehicle is parked. This electric steering lock device includes: a lock member movable between a lock position at which the lock member engages with a steering shaft of the vehicle and an unlock position at which the lock member disengages from the steering shaft; an electric motor which is an electric actuator configured to actuate the lock member, and a drive mechanism configured to convert a rotational force of an output shaft of the electric motor into a force making the lock member advance or retract.
In such an electric steering lock device, when the vehicle stops and a driver turns off an engine start switch with an engine running, a higher-level unit of the electric steering lock device detects this and stops the engine. Provided that the safety is confirmed, the higher-level unit sends a lock request to the electric steering lock device. Upon receipt of the lock request, the electric steering lock device drives the electric motor to move the lock member so that the lock member may engage with the steering shaft. Thus, rotation of the steering wheel is locked.
On the other hand, when the driver turns on the engine start switch with the vehicle, and therefore the engine, being stopped, the higher-level unit detects this and sends an unlock request to the electric steering lock device. Upon receipt of the unlock request, the electric steering lock device drives the electric motor to move the lock member so that the lock member may disengage from the steering shaft. The steering wheel is thus unlocked to enable steering maneuvers.
In this way, in order for the electric steering lock device to electrically lock and unlock the steering wheel, driving of the electric motor has to be controlled based on a detection whether the lock member is at the lock position or at the unlock position, and to detect this, a mechanism for defecting the position of the lock member is provided. For example, the following mechanism is used as this position detecting mechanism (see, for example, Japanese Patent Application Publication No. 2008-049908). Specifically, a magnet is attached to a movable member such as the lock member, and magnetic detection elements, such as Hall elements, are placed at a position corresponding to the lock position and at a position corresponding to the unlock position, respectively. Then, by causing the magnetic defection elements to detect the magnetic force of the magnet, it is detected whether the lock member is at the lock position or at the unlock position.
In the electric steering lock device, it has to be ensured that the lock member is at the unlock position for sure so that the engine may not be started with the rotation of the steering wheel being locked. As one of measures for ensuring that, multiple magnetic detection elements are placed at the position on the unlock side. In this method, a failure of one of the magnetic detection elements can be checked based on outputs of the other electric detection elements. Thus, false detection of the position of the lock member can be prevented.
However, in the method of placing multiple magnetic detection elements at the unlock-side position, when affected by an unexpected strong electromagnetic field, the multiple magnetic detection elements on the unlock side are all switched from an OFF state to an ON state even when the lock member is not actually at the unlock position. The lock member is thus falsely detected as having moved to the unlock state. Then, the lock member is stopped halfway, and the engine might be started with the rotation of the steering wheel still being locked.